Method and automatic device for measuring the content of a soluble component in a powdery product

ABSTRACT

A method for automatically determining the quantity of a soluble component in a powdery product is disclosed comprising providing a sample receiving container, weighing the sample receiving container, computing the weight of a predetermined quantity of solvent for the soluble component and introducing that predetermined quantity of solvent to the sample receiving container, introducing a predetermined quantity of the powdery product into the sample receiving container including the computed weight of solvent, weighing the solvent containing container with the predetermined quantity of powdery product and solvent therein, computing the weight of the predetermined quantity of powdery product, computing the weight ratio of the predetermined quantity of powdery product to the predetermined quantity of solvent, agitating the predetermined quantity of powdery product and solvent within the sample receiving container so as to create a solution thereof, determining an electrical characteristic of the solution, and correcting the electrical characteristic of the solution as a function of the weight ratio of the predetermined quantity of powdery product to the predetermined quantity of solvent therein.

BACKGROUND OF THE INVENTION

The present invention relates to a method of measuring the lime contentof a powdery product, comprising the steps of introducing a determinedquantity of the powdery product and a determined quantity of a solventinto a recipient, agitating this mixture so as to dissolve the lime inthe solvent, and measuring in this mixture an electrical characteristicrepresenting said lime content.

The invention also relates to a device for measuring the content of asoluble component in a powdery product, comprising at least onerecipient, means for dosing a given quantity of a solvent and bringingit to said recipient, means for dosing a given quantity of the powderyproduct and bringing it to the recipient, means for agitating thecontents of the recipient, means for measuring an electricalcharacteristic in the contents of the recipient, and means fordischarging the contents of the recipient after this measurement.

The invention applies particularly, but not exclusively, to themeasurement of the free lime content of cement or cement clinker.

In cement works such a measurement is regularly made on a sample ofclinker taken from the kiln exit, then cooled and crushed, with theobject of controlling the production, especially the burning process inthe kiln.

French Pat. No. 2 163 963 describes a method and a device for carryingout this measurement in a manner allowing automatic operation of acement plant kiln. One uses in this case a device comprising on one handa chamber, in which a mixture of the crushed clinker sample and heatedglycol is prepared and an electrical characteristic of this mixture ismeasured, and on the other hand means for supplying dosed volumes ofclinker and glycol to this compartment. The dosing and supply means forthe crushed clinker are described in more detail in French Pat. No. 2182 283 and comprise a calibrated assay crucible, into which the clinkeris poured and packed, then levelled to constitute the desired volume.This crucible is next brought mechanically by a mobile arm above thechamber to empty the clinker into it.

This operating mode and this device still have various drawbacks whichaffect the precision of the measurement and the reliability of theprocess, and hence also the quality of the clinker produced in the kilnin the case of automatic operation. First of all the density of thecrushed clinker sample may vary, in particular with the granulometry ofthe sample. This occurs especially in the case of malfunction of thekiln, producing an "unburnt" clinker whose grindability differs fromthat of normal clinker. As a result, the quantity of clinker introducedinto the measuring chamber also varies and the measurement is given anerroneous value. Now, it is precisely in such a case that the productionhas to be corrected.

On the other hand, the volumetric determination of the quantities withthis device does not allow for control in an automatic process. If oneof the supply devices malfunctions, the measurement may be effected onfalse quantities, for example if the calibrated assay crucible is notcompletely filled with clinker before levelling. The same applies in thecase of malfunction of the pump for glycol.

In addition, the measuring chamber is a complex and delicate instrument.In particular, its complete evacuation between two operating cycles isnot always ensured, because the valves may be obstructed. Thedisplacement of the mobile electrode which it contains is also subjectto faulty operation.

Consequently, the present invention has the object of meeting thesedrawbacks, by providing a method of the type mentioned in the preambleand allowing precise and reliable measurement of the lime content to beachieved, by means of a device including relatively simple and provencomponents. The invention shall particularly ensure highly reliableoperation of the successive measurements carried out during automaticoperating cycles of the device, in order to be fit for use in anautomatic system for controlling the production of the powdery product.

SUMMARY OF THE INVENTION

To this end, the measuring method according to the invention ischaracterized in that the weight of the powdery product introduced intothe recipient is measured, by weighing the recipient before and afterintroduction of this product, in that the weight ratio between therespective quantities of the powdery product and the solvent introducedinto the recipient is calculated, and in that the result of saidmeasurement of an electrical characteristic is corrected as a functionof this ratio.

The weight of said quantity of solvent is preferably also measured byweighing the recipient before and after introducing the solvent.

According to a preferred embodiment of the method, wherein automaticmeasuring cycles controlled by an electronic calculator are carried out,this calculator receives signals representing weighings, it calculatesthe respective weights of the product and the solvent, as well as saidweight ratio, and it corrects said measurement of an electricalcharacteristic in such a manner as to deliver at least one output signalrepresenting the lime content of the powdery product. This output signalis especially suitable for displaying the results of the measurementand/or the automatic operation of the plant for manufacturing thepowdery product.

With this preferred mode of the method, at least one calibration of theweighing means may be carried out during the automatic measuring cycle,while the calculator corrects the results of the weighings in accordancewith the calibration. On the other hand, the calculator mayautomatically modify a measuring cycle if one of the measured orcalculated weights lies outside a corresponding predetermined range.

The device according to the invention is adapted to allow this method tobe carried out and is characterized in that it includes means fordisplacing the recipient and means for weighing it.

According to a preferred embodiment of the device, the means fordisplacing the recipient comprise a clamp adapted to grip the recipientand mounted on a motorized support arranged for displacing the recipientalong a horizontal arc of a circle, for vertical translation and forpivoting round a substantially horizontal axis.

The means for weighing the recipient preferably include an electronicbalance. According to another variant, these means include a sensor witha strain gauge.

The means for dosing a given quantity of the solvent preferably includea positive displacement pump. The means for dosing a given quantity ofthe powdery product likewise include volumetric dosing means. Thesevolumetric dosing means need not ensure extremely precise dosing; theymay especially consist of a rotary plate equipped with a scraper.

The present invention and its advantages will be better understood bythe description of an embodiment, provided for dosing the free lime in asample of cement clinker, after crushing this sample. This descriptionis given below by way of a non-limiting example, with reference to theaccompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of the device according to theinvention, and

FIG. 2 is a schematic elevational view of the device represented in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the figures, the device represented essentiallyincludes a distributor 1 for the crushed clinker, an electronic balance2, an evacuating tank 3, a measuring unit 4, a glycol supply unit 5 anda manipulating robot 6 for displacing a measuring recipient 7. In thiscase the recipient 7 is a conventional beaker, but it may evidentlyconsist of any type of recipient open at the top and appropriate for itsfunction. The device further comprises a control panel 8 equipped with acalculator 9.

The distributor 1 is connected to the outlet of a clinker supply pipe10, through which the clinker samples taken from the exit of the kiln,then cooled and crushed, arrive in the direction of the arrow A, to ahopper 11. Under this hopper lies a rotary plate 12 drivenintermittently by a motor 13. A scraper consisting of two elements 14and 15 is disposed in a fixed position above the upper face of the plate12. The first element 14 includes a hole or a notch for forming on theplate a band of clinker of determined volume, while the second element15 is disposed obliquely in such a manner as to push this band out ofthe plate 12 and to tip into the recipient 7 brought below it. Theexcess material situated in front of the element 14 falls into adischarge hopper 16, from which it is periodically evacuated in thedirection of the arrow B by means of an ejector 17.

The balance 2 is an electronic precision balance, with a range of 100 to200 grams and a step of 1 mg. It is mounted at an appropriate height ona support 21 and is electrically connected to a calculator 9 to transmitthereto the results of each weighing.

As a variant, the balance 2 may be replaced by a sensor with a straingauage, which must then be automatically recalibrated at each measuringcycle, by depositing a standard weight 22 represented in dashed lines inthe drawing.

The evacuating tank 3 is open at the top, so that the contents of therecipient may be easily emptied into it. This tank is only representedschematically; it may consist for example of a simple barrel which isopen at the top and is periodically replaced, or by a more intricatereservoir equipped with filters and with an extraction pump forrecycling the glycol.

The glycol supply unit 5 is disposed near to the measuring unit 4. Inthe example illustrated here, it compares a glycol reservoir 51, mountedon a heating device 52 controlled by a thermostat, and a positivedisplacement pump 53, for example a peristaltic pump, which is connectedto the measuring unit 4 by a glycol distributing pipe 54. In themeasuring unit, the end of the pipe 54 is provided with a spout 55 forpouring the warm glycol into the recipient 7.

The measuring unit 4 includes a set of instruments 41 intended to beplunged into the contents of the recipient 7 during the process. Forthis purpose, the set of instruments 41 is mounted on a chassis 42 whichis vertically mobile along a wall support 43, by means of a small jack44 which may be for example an electric jack.

The set of instruments 41 is only represented schematically, because itsimply combines several instruments each of which is well known. Theseare in this case an agitator for mixing the glycol and the powderclinker in the recipient 7, a temperature regulator comprising a heatsensor and a heating element, for maintaining the mixture at a precisetemperature and communicating this temperature to the control means, anda pair of electrodes adapted to provide the electrical measurement,which is preferably a measurement of the conductivity of the mixture,but which may also be a measurement of a potential, of the pH or of asimilar characteristic.

As will be described below, the recipient 7 must be displaced severaltimes between the devices 1 to 4 during a measuring cycle. To this end,it is carried by a clamp 61 disposed at the end of a horizontal arm 62of a manipulating robot 6. This consists of an apparatus with threedegrees of displacement, of a type well known in material handlingengineering and essentially including a fixed base 63, a vertical column64 vertically mobile with respect to the base, in the direction of thedouble arrow C, and the arm 62 mounted at the top of the column 64 so asto swivel round the vertical axis of this column, according to the arrowD and through the action of a mechanism 65. The free end 66 of the arm62 carries the clamp 61 and is adapted to swivel around the horizontalaxis of this arm, in the direction of the double arrow E. A mechanismfor opening and closing the clamp 61 is accomodated in the arm 62. As isshown in FIG. 1, the manipulating robot 6 is installed at the center ofan arc of a circle 68 along which the elements 1 to 4 of the device aredistributed. In plan view, displacements of the recipient 7 all takeplace along this arc of a circle. In FIG. 1, the respective positions ofthe recipient 7 near to the different apparatuses 1 to 4 are indicatedby the corresponding positions of the axis of the arm 62, indicated bythe references 1', 2', 3' and 4. Another position 2" is indicated forthe case where the standard weight 22 is used.

With the method according to the present invention, an operating cycleof the device described above takes place as follows, while alloperations of this cycle are automatically controlled and checked fromthe control panel 8. At rest, the recipient 7 is filled with glycol andlies in the position 3' above the evacuating tank 3.

By pivoting the end 66 of the arm, the recipient is turned upside downand emptied into this tank, and next brought into the position 2" to bedeposited on the balance 2 and to be calibrated. The balance transmitsthe tare weight of the recipient 7 to the calculator 9. The manipulator6 next grasps the recipient 7 once more by the clamp 61 and brings ininto the position 4' for it to receive a dose of hot glycol, for example50 ml, delivered by the peristaltic pump 53 and the pipe 54. Therecipient is then brought back to the position 2" to be weighed on thebalance, while the calculator 9 then calculates the exact weight of theglycol dose by the difference between the weight of the recipient beforeand after introduction of the glycol.

The recipient is then brought to the position 1' and the rotary plate 12of the distributor 1 is brought into action for a duration correspondingto pouring out a given volume of powdery clinker into the recipient,this volume being determined so as to correspond approximately to onegram of clinker. To determine the exact weight of the quantity ofclinker introduced into the recipient, the latter is weighed once moreon the balance 2, while the calculator 9 again determines this weight bythe difference between the weighings before and after. The calculator 9also calculates the ratio between the weight of the glycol and theweight of the clinker. The recipient 7 is brought back into the position4' for the conductivity measurement. The set of instruments 41 islowered by the jack 44 down to the recipient, then the temperatureregulator is made to operate and the agitator is actuated for adetermined duration. Next, if the temperature lies in the requiredrange, the conductivity measurement is effected and transmitted to thecalculator 9, which corrects it as a function of the weight ratio of theclinker and the glycol and delivers a preferably numerical outputsignal, for display of the results on the panel 8 and for the controlmeans of the kiln in which the clinker is produced. The set ofinstruments 41 is then raised again and the recipient 7 is brought backinto the position 3' to empty its contents into the tank 3 in view ofrecycling the glycol. The recipient is then rinsed, while receiving inthe position 4' a new dose of glycol, which may possibly be stirred bythe agitator and which is then poured out into the tank 3, the recipient7 then remaining in the rest position at 3'.

In the case where the electronic balance 2 is replaced by a sensor witha strain gauge, the operating cycle further includes at least one phasefor calibrating this sensor, during which the recipient 7 is depositedby the clamp 61 in a stand-by position 1', while this clamp is used toseize the standard weight 22 in the position 2", to bring it into theposition 2' to be weighed, then setting it back in place.

The calculator 9 then determines the weight of the recipient as afunction of the weight indicated by the sensor for the standard 22.

With the method described above, as all results are transmitted to thecalculator 9 the latter may effect tests on these results and interruptor recommence the cycle if one of the values goes beyond thepredetermined range of tolerance.

One thus avoid the risks inherent in volumetric dosage according to theprior art, with which an insufficiency or an excess of one or the otherof the components went undetected.

This method allows complete freedom from the error in sampling of whichthe weight is known with precision. The measurement may moreover be maderepeatedly without taking particular precautions that the weight of thesubstances taken up in each sampling remain within predetermined limits.

A system in which the samples whose weight is too far away from adetermined value, fixed by the operator, are removed, is described inFrench Pat. No. 2,564,592. The drawback of such a system resides in thefact that several samples may possibly be rejected successively, forexample if the recipient used for collecting them is only incompletelyfilled due to any defect of the control means. The rejection of severalsuccessive samples entails a loss of measurements which may lead tofaults in production, given that the measurements are exploited toensure the automatic control of production.

Moreover, in the device described above, one only uses relatively simplemeans which are to a small extent subject to disturbance. In addition,these means are easily adapted to the installation of operationalcontrol means, for example sensors detecting the presence or absence orthe position of the recipient 7, as well as the quantities of clinker orglycol still available. One thus obtains a very great operating safetyand excellent reliability of the measurement results.

Tests have shown that, in a cement plant, a device according to theinvention is capable of carrying out a cycle every ten minutes, hencecorrecting burning of the clinker in the kiln practically in real time.

The present invention is not limited to the embodiment described aboveby way of example, but it extends to any modification or variant obviousto one skilled in the art. In particular, the device is not limited tothe measurement of the lime content in cement clinker, but it is fit foruse, with the appropriate modifications for the particular case, for anymeasurement of the content of a soluble component, in a powdery product.

I claim:
 1. An automatic method of determining the quantity of a solublecomponent in a powdery product comprising the steps of:(a) providing asample receiving container; (b) weighing said sample receivingcontainer; (c) computing the weight of a predetermined quantity of asolvent for said soluble component and introducing said predeterminedquantity of solvent into said sample receiving container; (d)introducing a predetermined quantity of said powdery product into saidsample receiving container including said computed weight of saidsolvent; (e) weighing said solvent receiving container with saidpredetermined quantity of said powdery product and said solvent therein;(f) computing the weight of said predetermined quantity of said powderyproduct; (g) computing the weight ratio of said predetermined quantityof said powdery product to said predetermined quantity of said solvent;(h) agitating said predetermined quantity of said powdery product andsaid predetermined quantity of said solvent within said sample receivingcontainer so as to create a solution of said soluble component in saidpowdery product; (i) determining an electrical characteristic of saidsolution of said soluble component in said powdery product; and (j)correcting said electrical characteristic of said solution as a functionof said weight ratio of said predetermined quantity of said powderyproduct to said predetermined quantity of said solvent.
 2. The methodaccording to claim 1, wherein said step (c) comprises individuallyintroducing said predetermined quantity of said solvent into said samplereceiving container, weighing said sample receiving container with saidpredetermined quantity of said solvent therein, and computing the weightof said predetermined quantity of said solvent.
 3. The method accordingto claim 1, wherein said solvent comprises a glycol, and wherein saidpredetermined characteristic comprises conductivity.
 4. The methodaccording to claim 3 including the step of terminating said method ifsaid weight of said sample receiving container as determined in step(b), or said weight of said predetermined quantity of said solvent asdetermined in step (c), or said weight of said predetermined quantity ofsaid powdery product as determined in step (f), are beyond apredetermined acceptability range.
 5. The method according to claim 3including the step of maintaining said glycol within a predeterminedtemperature range; and terminating said method if the temperature ofsaid glycol is not within said predetermined temperature range.
 6. Themethod according to claim 1, further including the steps ofautomatically repeating steps (a) through (j) at predetermined timeintervals.
 7. The method according to claim 1 including the additionalsteps of:(k) emptying said sample receiving container after step (j);and (l) rinsing said sample receiving container.
 8. The method of claim7 wherein said step (1) includes refilling said sample receivingcontainer with solvent, agitating said sample receiving container andemptying said sample receiving container.
 9. The method according toclaim 8 including recycling said solvent for continued use.